Differential force and touch sensing

ABSTRACT

An input device is configured to detect force being applied to an input region of the device by an input object, in addition to the position of the input object using touch sensing methods. Aspects include driving a force sensing electrode of the input device using an anti-guarding voltage alternating with a ground or guard voltage, while driving the touch sensing electrodes with a reference voltage, to obtain touch measurements, force measurements, interference measurements, double the force signal, and/o double the touch signal for differential touch and force detection. Aspects also include driving sensor electrodes using orthogonal signals and performing in-phase and quadrature demodulation of the received signal for simultaneous and independent touch and force measurements.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.62/330,042, filed Apr. 29, 2016, the entire contents of which areincorporated by reference herein.

BACKGROUND Field of the Disclosure

Aspects of this disclosure generally relate to capacitive sensing and,more particularly, sensing touch and force on an input surface usingcapacitive sensing.

Description of the Related Art

Input devices including proximity sensor devices (also commonly calledtouchpads or touch sensor devices) are widely used in a variety ofelectronic systems. A proximity sensor device typically includes asensing region, often demarked by a surface, in which the proximitysensor device determines the presence, location and/or motion of one ormore input objects. Proximity sensor devices may be used to provideinterfaces for the electronic system. For example, proximity sensordevices are often used as input devices for larger computing systems(such as opaque touchpads integrated in, or peripheral to, notebook ordesktop computers). Proximity sensor devices are also often used insmaller computing systems (such as touch screens integrated in cellularphones).

Some input devices have integrated force sensors. However, most forcesensor integrations require dedicated force sensor electrodes andassociated routing. The force sensor electrodes and associated routingundesirably add manufacturing and material cost for fabrication of theinput device, and often undesirably add to the thickness and or size ofthe touch and/or force sensing components. Moreover, adding routing foradditional force sensor electrodes undesirably consumes space within theinput device, thus leaving less space available for other componentswhich may reduce functionality. However, one problem with combiningsensors is distinguishing between the touch signal and the force signal.

Thus, there is a need for an improved input device that allowsdifferentiating between the touch and force signals, thereby enablingtouch and force sensing. Techniques for simultaneous touch and forcesensing are also desirable.

SUMMARY

This disclosure generally provides input devices, processing systems andmethods for differential touch and force sensing using anti-guarding andsimultaneous touch and force sensing using both in-phase and quadrature(I/Q) demodulation. Techniques herein allow for narrow bandwidth sensingsince they reduce latency of reporting and increase the accuracy ofcorrelation between the touch and force signals for fast motions (e.g.,relative to the sensor pitch and report rate).

Aspects of the present disclosure provide an input device. The inputdevice includes an input surface; at least one force electrode; aplurality of sensor electrodes disposed between the input surface andthe at least one force electrode, the plurality of sensor electrodesconfigured to deflect toward the at least one force electrode inresponse to a force applied to the input surface; and a processingsystem coupled to the plurality of sensor electrodes, the processingsystem configured to: drive the plurality of sensor electrodes with amodulated reference voltage; while driving the plurality of sensorelectrodes with the modulated reference voltage, drive the at least oneforce electrode by alternating between a guarding voltage modulation andan anti-guarding voltage modulation, wherein the guarding voltagemodulation is in-phase with respect to the modulated reference voltage,and wherein the anti-guarding voltage is out of phase with respect tothe modulated reference voltage; receive resulting signals comprisingeffects of user input upon the coupling of at least one of the modulatedreference voltage, the guarding voltage, or the anti-guarding voltage,the effects indicative of changes in capacitance of the plurality ofsensor electrodes; and determine both position information and forceinformation for an input object based on at least two of the resultingsignals.

Aspects of the present disclosure provide a processing system for aninput device. The processing system includes sensor circuitry configuredto: acquire first resulting signals by driving a plurality of sensorelectrodes with a first modulated voltage, the plurality of sensorelectrodes disposed between an input surface of the input device and aforce electrode and configured to deflect toward the force electrode inresponse to a force applied to the input surface; and acquire a secondresulting signal, while the plurality of sensor electrodes are drivenwith the first modulated voltage, by driving the force electrode with asecond modulated voltage, wherein the second modulated voltage ispartially out of phase (e.g., 90 degrees) with respect to the firstmodulated voltage; and a determination module, coupled to the sensorcircuitry, configured to: determine positional information for an inputobject based on the first and second resulting signals; and determineforce information for the input object based on the second resultingsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toaspects, some of which are illustrated in the appended drawings. It isto be noted, however, that the appended drawings illustrate only typicalaspects of this disclosure and are therefore not to be consideredlimiting of its scope, for the disclosure may admit to other equallyeffective aspects.

FIG. 1 is a block diagram of an exemplary input device, according to oneaspect described herein.

FIGS. 2A-2B illustrate portions of exemplary patterns of sensingelements according to aspects described herein.

FIG. 3 is a block diagram depicting a cross-section of an input deviceaccording to an aspect.

FIG. 4 is a block diagram depicting a simplified cross-section of anexample input device with an alternating guard and anti-guard signalapplied to the internal conductive housing of the input device,according to an aspect.

FIG. 5 is a block diagram depicting a simplified cross-section of anexample input device with an alternating ground and anti-guard signalapplied to the internal metal housing of the input device, according toan aspect.

FIG. 6 is a flow diagram illustrating example operations fordifferential touch and force sensing using an anti-guarding signal,according to an aspect.

FIG. 7 is a block diagram depicting a simplified cross-section of anexample input device showing driving the electrodes with a modulatedsensing signal to acquire touch-to-sensor capacitive coupling andbackground capacitance, according to an aspect.

FIG. 8 is a block diagram depicting a simplified cross-section of anexample input device showing driving the electrodes with orthogonalmodulated sensing signals to acquire touch-to-sensor capacitive couplingand background capacitance, according to an aspect.

FIG. 9A-9B are block diagrams illustrating example signal paths for bothin-phase and/or quadrature demodulation of resulting signals, andguarding/anti-guarding sensing according to aspects described herein.

FIG. 10 is a flow diagram illustrating example operations forsimultaneous touch and force sensing using in-phase and quadraturedemodulation, according to an aspect.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation. The drawings referred to here should not be understood asbeing drawn to scale unless specifically noted. Also, the drawings areoften simplified and details or components omitted for clarity ofpresentation and explanation. The drawings and discussion serve toexplain principles discussed below, where like designations denote likeelements.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the disclosure or its application and uses.Furthermore, there is no intention to be bound by any expressed orimplied theory presented in the preceding technical field, background,brief summary or the following detailed description.

Various aspects of the present disclosure provide input devices,processing systems and methods for differential touch sensing and forcesensing using guarding, anti-guarding and for simultaneous touch andforce sensing using orthogonal sensing signals in-phase and quadrature(i.e., I/Q) demodulation. As utilized herein, capacitive sensing isdescribed as a touch sensing technique utilizing information receivedfrom capacitive sensor electrodes at least some of which may becombination electrodes used for both capacitive touch sensing anddisplay updating, while force sensing is described as utilizinginformation transmitted by force sensor electrodes to determine forcethat an input object exerts against the input device.

Input devices having a force detector are generally based on a bendingeffect caused by a force applied to the input device by an input object.The bending results in a deflection from equilibrium of at least aportion of the sensor electrodes in the input device. For example, insome aspects, the deflection of sensor electrode(s) due to the appliedforce changes the distance between at least one of the sensor electrodesand the one or more force electrodes, which can be detected as a changein capacitance. Due to the mechanical nature of the bending effect, thesame force applied at different positions on the input surface canreport different force levels. For example, force sensor datacorresponding to the center of the input surface may be elevatedrelative to data from the edges or corners of the input surface. Toaddress this problem, position compensation is applied when determiningforce level information using the force sensor data. Where off-screencapacitive buttons are present force information may also be extractedbased on the location of the user input on the button and the effect offorce sensed by the system within the sensing region 120.

However, distinguishing between touch and force signals can bedifficult. Accordingly, aspects of the present disclosure provide aprocessing system that uses different modulation phases forindependently measuring force and touch signals. For example, guardingand anti-guarding signals to double the signal for differential touchand force sensing or in-phase and quadrature demodulation forsimultaneous and independent touch and force measurements.

FIG. 1 is a block diagram of an exemplary input device 100, inaccordance with aspects of the disclosure. The input device 100 may beconfigured to provide input to an electronic system (not shown). As usedin this document, the term “electronic system” (or “electronic device”)broadly refers to any system capable of electronically processinginformation. Some non-limiting examples of electronic systems includepersonal computers of all sizes and shapes, such as desktop computers,laptop computers, netbook computers, tablets, web browsers, e-bookreaders, and personal digital assistants (PDAs). Additional exampleelectronic systems include composite input devices, such as physicalkeyboards that include input device 100 and separate joysticks or keyswitches. Further example electronic systems include peripherals such asdata input devices (including remote controls and mice), and data outputdevices (including display screens and printers). Other examples includeremote terminals, kiosks, and video game machines (e.g., video gameconsoles, portable gaming devices, and the like). Other examples includecommunication devices (including cellular phones, such as smart phones),and media devices (including recorders, editors, and players such astelevisions, set-top boxes, music players, digital photo frames, anddigital cameras). Additionally, the electronic system could be a host ora slave to the input device.

The input device 100 can be implemented as a physical part of theelectronic system, or can be physically separate from the electronicsystem. As appropriate, the input device 100 may communicate with partsof the electronic system using any one or more of the following: buses,networks, and other wired or wireless interconnections. Examples includeI²C, SPI, PS/2, Universal Serial Bus (USB), MIPI DSI, eDP-AUX channel,Bluetooth, RF, and IRDA.

In FIG. 1, the input device 100 is shown as a proximity sensor device(also often referred to as a “touchpad” or a “touch sensor device”)configured to sense input provided by one or more input objects 140 in asensing region 120. Example input objects include fingers and styli, asshown in FIG. 1.

Sensing region 120 encompasses any space above, around, in and/or nearthe input device 100 in which the input device 100 is able to detectuser input (e.g., user input provided by one or more input objects 140).The sizes, shapes, and locations of particular sensing regions may varywidely from embodiment to embodiment. In some embodiments, the sensingregion 120 extends from a surface of the input device 100 in one or moredirections into space until signal-to-noise ratios prevent sufficientlyaccurate object detection. The distance to which this sensing region 120extends in a particular direction, in various embodiments, may be on theorder of less than a millimeter, millimeters, centimeters, or more, andmay vary significantly with the type of sensing technology used and theaccuracy desired. Thus, some embodiments sense input that comprises nocontact with any surfaces of the input device 100, contact with an inputsurface (e.g. a touch surface) of the input device 100, contact with aninput surface of the input device 100 coupled with some amount ofapplied force or pressure, and/or a combination thereof. In variousembodiments, input surfaces may be provided by surfaces of casingswithin which the sensor electrodes reside, by face sheets applied overthe sensor electrodes or any casings, etc. In some embodiments, thesensing region 120 has a rectangular shape when projected onto an inputsurface of the input device 100. In some embodiments with combinationelectrodes the sensing region 120 may be defined by the display region.

The input device 100 may utilize any combination of sensor componentsand sensing technologies to detect user input in the sensing region 120.The input device 100 comprises one or more sensing elements fordetecting user input. As several non-limiting examples, the input device100 may use capacitive, elastive, resistive, inductive, magnetic,acoustic, ultrasonic, and/or optical techniques.

Some implementations are configured to provide images that span one,two, three, or higher dimensional spaces. Some implementations areconfigured to provide projections of input along particular axes orplanes.

In some capacitive implementations of the input device 100, voltage orcurrent is applied to create an electric field. Nearby input objectscause changes in the electric field, and produce detectable changes incapacitive coupling that may be detected as changes in voltage, current,accumulated charge, or the like.

Some capacitive implementations utilize arrays or other regular orirregular patterns of capacitive sensing elements to create electricfields. In some capacitive implementations, separate sensing elementsmay be ohmically shorted together to form larger sensor electrodes. Somecapacitive implementations utilize resistive sheets, which may beuniformly resistive, metal mesh, Indium Tin Oxide (ITO), etc.

Some capacitive implementations utilize “self-capacitance” (or “absolutecapacitance”) sensing methods based on changes in the capacitivecoupling between sensor electrodes and an input object. In variousembodiments, an input object near the sensor electrodes alters theelectric field near the sensor electrodes, thus changing the measuredcapacitive coupling. In one implementation, an absolute capacitancesensing method operates by modulating sensor electrodes with respect toa reference voltage (e.g. system ground), and by detecting thecapacitive coupling between the sensor electrodes and input objects.

Some capacitive implementations utilize “mutual capacitance” (or“transcapacitance”) sensing methods based on changes in the capacitivecoupling between sensor electrodes. In various embodiments, an inputobject near the sensor electrodes alters the electric field between thesensor electrodes, thus changing the measured capacitive coupling. Inone implementation, a transcapacitive sensing method operates bydetecting the capacitive coupling between one or more transmitter sensorelectrodes (also “transmitter electrodes” or “transmitters”) and one ormore receiver sensor electrodes (also “receiver electrodes” or“receivers”). Transmitter sensor electrodes may be modulated relative toa reference voltage (e.g., system ground) to transmit transmittersignals. Receiver sensor electrodes may be held substantially constantrelative to the reference voltage to facilitate receipt of resultingsignals. A resulting signal may comprise effect(s) due to user inputcoupling corresponding to one or more transmitter signals, and/or to oneor more sources of environmental interference (e.g. otherelectromagnetic signals). Sensor electrodes may be dedicatedtransmitters or receivers, or may be configured to both transmit andreceive.

In FIG. 1, a processing system 110 is shown as part of the input device100. The processing system 110 is configured to operate the hardware ofthe input device 100 to detect input in the sensing region 120. Theprocessing system 110 comprises parts of or all of one or moreintegrated circuits (ICs) and/or other circuitry components. Forexample, a processing system for a mutual capacitance sensor device maycomprise transmitter circuitry configured to transmit signals withtransmitter sensor electrodes, and/or receiver circuitry configured toreceive signals with receiver sensor electrodes). In some embodiments,the processing system 110 also comprises electronically-readableinstructions, such as firmware code, software code, and/or the like. Insome embodiments, components composing the processing system 110 arelocated together, such as near sensing element(s) of the input device100. In other embodiments, components of processing system 110 arephysically separate with one or more components close to sensingelement(s) of input device 100, and one or more components elsewhere.For example, the input device 100 may be a peripheral coupled to adesktop computer, and the processing system 110 may comprise softwareconfigured to run on a central processing unit of the desktop computerand one or more ICs (perhaps with associated firmware) separate from thecentral processing unit. As another example, the input device 100 may bephysically integrated in a phone, and the processing system 110 maycomprise circuits and firmware that are part of a main processor of thephone. In some embodiments, the processing system 110 is dedicated toimplementing the input device 100. In other embodiments, the processingsystem 110 also performs other functions, such as operating displayscreens, driving haptic actuators, etc.

The processing system 110 may be implemented as a set of modules thathandle different functions of the processing system 110. Each module maycomprise circuitry that is a part of the processing system 110,firmware, software, or a combination thereof. In various embodiments,different combinations of modules may be used. Example modules includehardware operation modules for operating hardware such as sensorelectrodes and display screens, data processing modules for processingdata such as sensor signals and positional information, and reportingmodules for reporting information. Further example modules includesensor operation modules configured to operate sensing element(s) todetect input, identification modules configured to identify gesturessuch as mode changing gestures, and mode changing modules for changingoperation modes.

In some embodiments, the processing system 110 responds to user input(or lack of user input) in the sensing region 120 directly by causingone or more actions. Example actions include changing operation modes,as well as GUI actions such as cursor movement, selection, menunavigation, and other functions. In some embodiments, the processingsystem 110 provides information about the input (or lack of input) tosome part of the electronic system (e.g. to a central processing systemof the electronic system that is separate from the processing system110, if such a separate central processing system exists). In someembodiments, some part of the electronic system processes informationreceived from the processing system 110 to act on user input, such as tofacilitate a full range of actions, including mode changing actions andGUI actions. In some embodiments, some part of the system responds to ameasurement of interference to select a sensing frequency.

For example, in some embodiments, the processing system 110 operates thesensing element(s) of the input device 100 to produce electrical signalsindicative of input (or lack of input) in the sensing region 120. Theprocessing system 110 may perform any appropriate amount of processingon the electrical signals in producing the information provided to theelectronic system. For example, the processing system 110 may digitizeanalog electrical signals obtained from the sensor electrodes. Asanother example, the processing system 110 may perform filtering orother signal conditioning. As yet another example, the processing system110 may subtract or otherwise account for a baseline, such that theinformation reflects a difference between the electrical signals and thebaseline. As yet further examples, the processing system 110 maydetermine positional information, recognize inputs as commands,recognize handwriting, and the like.

“Positional information” as used herein broadly encompasses absoluteposition, relative position, velocity, acceleration, and other types ofspatial information. Exemplary “zero-dimensional” positional informationincludes near/far or contact/no contact information. Exemplary“one-dimensional” positional information includes positions along anaxis. Exemplary “two-dimensional” positional information includesmotions in a plane. Exemplary “three-dimensional” positional informationincludes instantaneous or average velocities in space. Further examplesinclude other representations of spatial information. Historical dataregarding one or more types of positional information may also bedetermined and/or stored, including, for example, historical data thattracks position, motion, or instantaneous velocity over time.

In some embodiments, the input device 100 is implemented with additionalinput components that are operated by the processing system 110 or bysome other processing system. These additional input components mayprovide redundant functionality for input in the sensing region 120, orsome other functionality. FIG. 1 shows buttons 130 near the sensingregion 120 that can be used to facilitate selection of items using theinput device 100. The buttons 130 may be capacitively sensed and forcedata may be combined with button location and activation data todetermine reporting (e.g. intentional button press). Other types ofadditional input components include sliders, balls, wheels, switches,and the like. Conversely, in some embodiments, the input device 100 maybe implemented with no other input components.

In some embodiments, the input device 100 comprises a touch screeninterface, and the sensing region 120 overlaps at least part of anactive area of a display screen. For example, the input device 100 maycomprise substantially transparent sensor electrodes overlaying thedisplay screen and provide a touch screen interface for the associatedelectronic system. The display screen may be any type of dynamic displaycapable of displaying a visual interface to a user, and may include anytype of light emitting diode (LED), organic LED (OLED), cathode ray tube(CRT), liquid crystal display (LCD), plasma, electroluminescence (EL),or other display technology. The input device 100 and the display screenmay share physical elements. For example, some embodiments may utilizesome of the same electrical components for displaying and sensing (e.g.,an Active Matrix (e.g., a rectangular array) of Thin Film a-Sitransistors for AMOLED and AMLCD, etc.). As another example, the displayscreen of the display 180 may be operated in part or in total by theprocessing system 110.

In various embodiments, the input device 100 may comprise one or moresensor electrodes configured for both display updating and inputsensing. For example, at least one sensor electrodes that are used forinput sensing may comprise one or more display electrodes of the displaydevice that are used in updating the display. Further, the displayelectrode may comprise one or more of segments of a Vcom electrode(common electrodes), source drive lines (electrodes), gate line(electrodes), an anode sub-pixel electrode or cathode pixel electrode,or any other display element. These display electrodes may be disposedon an appropriate display screen substrate. For example, the displayelectrodes may be disposed on a transparent substrate (a glasssubstrate, TFT glass, or any other transparent material) in some displayscreens (e.g., In Plane Switching (IPS), Fringe Field Switching (FFS) orPlane to Line Switching (PLS) Organic Light Emitting Diode (OLED)), onthe bottom of the color filter glass of some display screens (e.g.,Patterned Vertical Alignment (PVA) Multi-domain Vertical Alignment(MVA), IPS and FFS), over an cathode layer (OLED), etc. In suchembodiments, the display electrode can also be referred to as a“combination electrode”, since it performs multiple functions. Invarious embodiments, each of the sensor electrodes comprises one or moredisplay electrodes associated with a pixel or sub pixel. In otherembodiments, at least two sensor electrodes may share at least onedisplay electrode associated with a pixel or sub-pixel.

In various embodiments, a first sensor electrode comprises one or moredisplay electrodes configured for display updating and capacitivesensing and a second sensor electrode may be configured for capacitivesensing and not for display updating. The second sensor electrode may bedisposed between substrates of the display device or external from thedisplay device. In some embodiments, all of the sensor electrodes maycomprise one or more display electrodes configured for display updatingand capacitive sensing.

Processing system 110 may be configured to perform input sensing anddisplay updating during at least partially overlapping periods. Forexample, a processing system 110 may simultaneously drive a firstdisplay electrode for both display updating and input sensing. Inanother example, processing system 110 may simultaneously drive a firstdisplay electrode for display updating and a second display electrodefor input sensing. In some embodiments, processing system 110 inconfigured to perform input sensing and display updating duringnon-overlapping periods. The non-overlapping periods may be referred toas non-display update periods. The non-display update periods may occurbetween display line update periods of common display frame and be atleast as long as a display line update period. Further, the non-displayupdate periods may occur between display line update periods of a commondisplay frame and be one of longer than or shorter than a display lineupdate period. In some embodiments, the non-display update periods mayoccur at the beginning of a display frame and/or between display frames.Processing system 110 may be configured to drive one or more of thesensor electrodes and/or the display electrodes with a shield signal.The shield signal may comprise one of a constant voltage signal or avarying voltage signal (guard signal). Further, one or more of thesensor electrodes and/or display electrodes may be electrically floated.

It should be understood that while many embodiments of the invention aredescribed in the context of a fully functioning apparatus, themechanisms of the present invention are capable of being distributed asa program product (e.g., software) in a variety of forms. For example,the mechanisms of the present invention may be implemented anddistributed as a software program on information bearing media that arereadable by electronic processors (e.g., non-transitorycomputer-readable and/or recordable/writable information bearing mediareadable by the processing system 110). Additionally, the embodiments ofthe present invention apply equally regardless of the particular type ofmedium used to carry out the distribution. Examples of non-transitory,electronically readable media include various discs, memory sticks,memory cards, memory modules, and the like. Electronically readablemedia may be based on flash, optical, magnetic, holographic, or anyother storage technology.

FIG. 2A illustrates a portion of an exemplary pattern of sensingelements according to some embodiments. For clarity of illustration anddescription, FIG. 2A shows the sensing elements in a pattern of simplerectangular electrodes and does not show various components, such asvarious interconnects between the sensing elements and the processingsystem 110 or joining sensing elements (e.g. jumpers, vias, etc.). Anelectrode pattern 250A comprises a first plurality of sensor electrodes260 (260-1, 260-2, 260-3, . . . 260-n), and a second plurality of sensorelectrodes 270 (270-1, 270-2, 270-3, . . . 270-m) disposed over thefirst plurality of electrodes 260. In some designs the electrodes may bepatterned to minimize overlap area and/or increase fringing capacitance.In the example shown, n=m=4, but in general n and m are each positiveintegers and not necessarily equal to each other. In variousembodiments, the first plurality of sensor electrodes 260 are operatedas a plurality of transmitter electrodes (referred to specifically as“transmitter electrodes 260”), and the second plurality of sensorelectrodes 270 are operated as a plurality of receiver electrodes(referred to specifically as “receiver electrodes 270”). In anotherembodiment, one plurality of sensor electrodes may be configured totransmit and receive and the other plurality of sensor electrodes mayalso be configured to transmit and receive. In yet another embodiment,the processing system 110 receives resulting signals with one or moresensor electrodes of the first and/or second plurality of sensorelectrodes while the one or more sensor electrodes are modulated withabsolute capacitive sensing signals. The first plurality of sensorelectrodes 260, the second plurality of sensor electrodes 270, or bothcan be disposed within the sensing region 120. The electrode pattern250A can be coupled to the processing system 110.

The first plurality of electrodes 260 and the second plurality ofelectrodes 270 are typically ohmically isolated from each other. Thatis, one or more insulators separate the first plurality of electrodes260 and the second plurality of electrodes 270 and prevent them fromelectrically shorting to each other. In some embodiments, the firstplurality of electrodes 260 and the second plurality of electrodes 270are separated by insulative material disposed between them at cross-overareas; in such constructions, the first plurality of electrodes 260and/or the second plurality of electrodes 270 can be formed with jumpersconnecting different portions of the same electrode. In someembodiments, the first plurality of electrodes 260 and the secondplurality of electrodes 270 are separated by one or more layers ofinsulative material. In such embodiments, the first plurality ofelectrodes 260 and the second plurality of electrodes 270 can bedisposed on separate layers of a common substrate. In some otherembodiments, the first plurality of electrodes 260 and the secondplurality of electrodes 270 are separated by one or more substrates; forexample, the first plurality of electrodes 260 and the second pluralityof electrodes 270 can be disposed on opposite sides of the samesubstrate, or on different substrates that are laminated together. Insome embodiments, the first plurality of electrodes 260 and the secondplurality of electrodes 270 can be disposed on the same side of a singlesubstrate.

The areas of localized capacitive coupling between the first pluralityof sensor electrodes 260 and the second plurality sensor electrodes 270may form an array of “capacitive pixels” of a “capacitive image.” Thecapacitive coupling between sensor electrodes of the first and secondpluralities 260 and 270 changes with the proximity and motion of inputobjects in the sensing region 120. Further, in various embodiments, thelocalized capacitive coupling between each of the first plurality ofsensor electrodes 260 and the second plurality of sensor electrodes 270and an input object may be termed “capacitive pixels” of a “capacitiveimage.” In some embodiments, the localized capacitive coupling betweeneach one of the first plurality of sensor electrodes 260 and the secondplurality of sensor electrodes 270 and an input object may be termed“capacitive measurements” of a “capacitive profile.”

The processing system 110 can include a sensor module 208 having sensorcircuitry 204. The sensor circuitry 204 operates the electrode pattern250A to receive resulting signals from electrodes in the electrodepattern using a capacitive sensing signal having a sensing frequency.For example, the sensor circuitry 204 can include analog front end(s)(AFEs) 226 that receive the resulting signals from the sensorelectrodes. The processing system 110 can include a processing module220 configured to determine capacitive measurements from the resultingsignals. The processing module 220 can include processor circuitry 222,such as a digital signal processor (DSP), microprocessor, or the like.The processing module 220 can include software and/or firmwareconfigured for execution by the processor circuitry 222 to implement thefunctions described herein. Alternatively, some or all of the functionsof the processor module 220 can be implemented entirely in hardware(e.g., using integrated circuitry). The processing module 220 can trackchanges in capacitive measurements to detect input object(s) in thesensing region 120. The processing system 110 can include other modularconfigurations, and the functions performed by the sensor module 208 andthe processing module 220 can, in general, be performed by one or moremodules or circuits in the processing system 110. The processing system110 can include other modules and circuits, and can perform otherfunctions as described in some embodiments below. The processing system110 can include output generator(s) 224 that couple modulated signals tothe sensing electrodes 260 and/or to the force electrode(s) 212. Theoutput generator(s) 224 can include optional AFE(s) 228 that receivesthe resulting signals from the force electrode(s) 212.

The processing system 110 can operate in absolute capacitive sensingmode or transcapacitive sensing mode. In absolute capacitive sensingmode, receiver(s) in the sensor circuitry 204 measure voltage, current,or charge on sensor electrode(s) in the electrode pattern 250A while thesensor electrode(s) are modulated with absolute capacitive sensingsignals to generate the resulting signals. The processing module 220generates absolute capacitive measurements from the resulting signals.The processing module 220 can track changes in absolute capacitivemeasurements to detect input object(s) in the sensing region 120.

In transcapacitive sensing mode, transmitter(s) in the sensor circuitry204 drive one or more of the first plurality of electrodes 260 with thecapacitive sensing signal (also referred to as a transmitter signal ormodulated signal in the transcapacitive sensing mode). Receiver(s) inthe sensor circuitry 204 measure voltage, current, or charge on one ormore of the second plurality of electrodes 270 to generate the resultingsignals. The resulting signals comprise the effects of the capacitivesensing signal and input object(s) in the sensing region 120. Theprocessing module 220 generates transcapacitive measurements from theresulting signals. The processing module 220 can track changes intranscapacitive measurements to detect input object(s) in the sensingregion 120.

In some embodiments, the processing system 110 “scans” the electrodepattern 250A to determine capacitive measurements. In thetranscapacitive sensing mode, the processing system 110 can drive thefirst plurality of electrodes 260 to transmit transmitter signal(s). Theprocessing system 110 can operate the first plurality of electrodes 260such that one transmitter electrode transmits at one time, or multipletransmitter electrodes transmit at the same time. Where multipletransmitter electrodes transmit simultaneously, these multipletransmitter electrodes may transmit the same transmitter signal andeffectively produce a larger transmitter electrode, or these multipletransmitter electrodes may transmit different transmitter signals. Forexample, multiple transmitter electrodes may transmit differenttransmitter signals according to one or more coding schemes that enabletheir combined effects on the resulting signals of the second pluralityof electrodes 270 to be independently determined. In the absolutecapacitive sensing mode, the processing system 110 can receive resultingsignals from one sensor electrode 260, 270 at a time, or from aplurality of sensor electrodes 260, 270 at a time. In either mode, theprocessing system 110 can operate the second plurality of electrodes 270singly or collectively to acquire resulting signals. In absolutecapacitive sensing mode, the processing system 110 can concurrentlydrive all electrodes along one or more axes. In some examples, theprocessing system 110 can drive electrodes along one axis (e.g., alongthe first plurality of sensor electrodes 260) while electrodes alonganother axis are driven with a shield signal, guard signal, or the like.In some examples, some electrodes along one axis and some electrodesalong the other axis can be driven concurrently.

In the transcapacitive sensing mode, the processing system 110 can usethe resulting signals to determine capacitive measurements at thecapacitive pixels. A set of measurements from the capacitive pixels forma “capacitive image” (also “capacitive frame”) representative of thecapacitive measurements at the pixels. The processing system 110 canacquire multiple capacitive images over multiple time periods, and candetermine differences between capacitive images to derive informationabout input in the sensing region 120. For example, the processingsystem 110 can use successive capacitive images acquired over successiveperiods of time to track the motion(s) of one or more input objectsentering, exiting, and within the sensing region 120 or to determine nouser inputs are present to enter a low power mode.

In absolute capacitive sensing mode, the processing system 110 can usethe resulting signals to determine capacitive measurements along an axisof the sensor electrodes 260 and/or an axis of the sensor electrodes270. A set of such measurements forms a “capacitive profile”representative of the capacitive measurements along the axis. Theprocessing system 110 can acquire multiple capacitive profiles along oneor both of the axes over multiple time periods and can determinedifferences between capacitive profiles to derive information aboutinput in the sensing region 120. For example, the processing system 110can use successive capacitive profiles acquired over successive periodsof time to track location or proximity of input objects within thesensing region 120. In other embodiments, each sensor can be acapacitive pixel of a capacitive image and the absolute capacitivesensing mode can be used to generate capacitive image(s) in addition toor in place of capacitive profiles.

The baseline capacitance of the input device 100 is the capacitive imageor capacitive profile associated with no input object in the sensingregion 120. The baseline capacitance changes with the environment andoperating conditions, and the processing system 110 can estimate thebaseline capacitance in various ways. For example, in some embodiments,the processing system 110 takes “baseline images” or “baseline profiles”when no input object is determined to be in the sensing region 120, anduses those baseline images or baseline profiles as estimates of baselinecapacitances. The processing module 220 can account for the baselinecapacitance in the capacitive measurements and thus the capacitivemeasurements can be referred to as “delta capacitive measurements”.Thus, the term “capacitive measurements” as used herein encompassesdelta-measurements with respect to a determined baseline.

In some touch screen embodiments, at least one of the first plurality ofsensor electrodes 260 and the second plurality of sensor electrodes 270comprise one or more display electrodes of a display device 280 used inupdating a display of a display screen, such as one or more segments ofa “Vcom” electrode (common electrodes), gate electrodes, sourceelectrodes, anode electrode and/or cathode electrode. These displayelectrodes may be disposed on an appropriate display screen substrate.For example, the display electrodes may be disposed on a transparentsubstrate (a glass substrate, TFT glass, or any other transparentmaterial) in some display screens (e.g., In Plane Switching (IPS) orPlane to Line Switching (PLS) Organic Light Emitting Diode (OLED)), onthe bottom of the color filter glass of some display screens (e.g.,Patterned Vertical Alignment (PVA) or Multi-domain Vertical Alignment(MVA)), over an emissive layer (backlight), etc. The display electrodescan also be referred to as “combination electrodes,” since the displayelectrodes perform functions of display updating and capacitive sensing.In various embodiments, each sensor electrode of the first and secondplurality of sensor electrodes 260 and 270 comprises one or morecombination electrodes. In other embodiments, at least two sensorelectrodes of the first plurality of sensor electrodes 260 or at leasttwo sensor electrodes of the second plurality of sensor electrodes 270may share at least one combination electrode. Furthermore, in oneembodiment, both the first plurality of sensor electrodes 260 and thesecond plurality electrodes 270 are disposed within a display stack onthe display screen substrate. Additionally, at least one of the sensorelectrodes 260, 270 in the display stack may comprise a combinationelectrode. However, in other embodiments, only the first plurality ofsensor electrodes 260 or the second plurality of sensor electrodes 270(but not both) are disposed within the display stack, while other sensorelectrodes are outside of the display stack (e.g., disposed on anopposite side of a color filter glass away from the active matrixtransistors).

In an embodiment, the processing system 110 comprises a singleintegrated controller, such as an application specific integratedcircuit (ASIC), having the sensor module 208, the processing module 220,and any other module(s) and/or circuit(s). In another embodiment, theprocessing system 110 can include a plurality of integrated circuits,where the sensor module 208, the processing module 220, and any othermodule(s) and/or circuit(s) can be divided among the integratedcircuits. For example, the sensor module 208 can be on one integratedcircuit, and the processing module 220 and any other module(s)and/circuit(s) can be one or more other integrated circuits. In someembodiments, a first portion of the sensor module 208 can be on oneintegrated circuit and a second portion of the sensor module 208 can beon second integrated circuit. In such embodiments, at least one of thefirst and second integrated circuits comprises at least portions ofother modules such as a display driver module and/or a display drivermodule.

FIG. 2B illustrates a portion of another exemplary pattern of sensingelements according to some embodiments. For clarity of illustration anddescription, FIG. 2B presents the sensing elements in a matrix ofrectangles and does not show various components, such as variousinterconnects between the processing system 110 and the sensingelements. An electrode pattern 250B comprises a plurality of sensorelectrodes 210 disposed in a rectangular matrix (e.g., a rectangulararray). The electrode pattern 250B comprises sensor electrodes 210_(J,K) (referred to collectively as sensor electrodes 210) arranged in Jrows and K columns, where J and K are positive integers, although one ofJ and K may be enumerated as zero. It is contemplated that the electrodepattern 250B may comprise other patterns of the sensor electrodes 210,such as polar arrays, repeating patterns, non-repeating patterns,non-uniform arrays a single row or column, or other suitablearrangement. Further, the sensor electrodes 210 may be any shape, suchas circular, rectangular, diamond, star, square, nonconvex, convex,nonconcave concave, etc. Further, the sensor electrodes 210 may besub-divided into a plurality of distinct sub-electrodes. The electrodepattern 250 is coupled to the processing system 110.

The sensor electrodes 210 are typically ohmically isolated from oneanother. Additionally, where a sensor electrode 210 includes multiplesub-electrodes, the sub-electrodes may be ohmically isolated from eachother. Furthermore, in one embodiment, the sensor electrodes 210 may beohmically isolated from a grid electrode 218 that is between the sensorelectrodes 210. In one example, the grid electrode 218 may surround oneor more of the sensor electrodes 210, which are disposed in windows 216of the grid electrode 218. In some embodiments, the electrode pattern250B can include more than one grid electrode 218. In some embodiments,the grid electrode 218 can have one or more segments. The grid electrode218 may be used as a shield or to carry a guarding signal for use whenperforming capacitive sensing with the sensor electrodes 210.Alternatively or additionally, the grid electrode 218 may be used assensor electrode when performing capacitive sensing. Furthermore, thegrid electrode 218 may be co-planar with the sensor electrodes 210, butthis is not a requirement. For instance, the grid electrode 218 may belocated on a different substrate or on a different side of the samesubstrate as the sensor electrodes 210. The grid electrode 218 isoptional and in some embodiments, the grid electrode 218 is not present.

In a first mode of operation, the processing system 110 can use at leastone sensor electrode 210 to detect the presence of an input object viaabsolute capacitive sensing. The sensor circuitry 204 can measurevoltage, charge, or current on sensor electrode(s) 210 to obtainresulting signals indicative of a capacitance between the sensorelectrode(s) 210 and an input object. The processing module 220 uses theresulting signals to determine absolute capacitive measurements. Withthe electrode pattern 250B, the absolute capacitive measurements can beused to form capacitive images. To sense the full array of electrodes210 sensor circuitry 204 may include multiplexors to scan through themand select which subset of electrodes to connect to AFEs 226 and whichto connect to a guard signal.

In a second mode of operation, the processing system 110 can use groupsof the sensor electrodes 210 to detect presence of an input object viatranscapacitive sensing. The sensor circuitry 204 can drive at least oneof the sensor electrodes 210 with a transmitter signal, and can receivea resulting signal from at least one other of the sensor electrodes 210.The processing module 220 uses the resulting signals to determinetranscapacitive measurements and form capacitive images.

The input device 100 may be configured to operate in any one of themodes described above. The input device 100 may also be configured toswitch between any two or more of the modes described above. Theprocessing system 110 can be configured as described above with respectto FIG. 2A.

In some embodiments, the processing system 110 is further configured todetermine force information for an input object. As shown in FIGS.2A-2B, the processing system 110 can be further coupled to one or moreforce electrodes 212. The processing system 110 can determine the forceinformation in response to capacitive measurements obtained using sensorelectrodes of the input device 100, one or more force electrode(s) 212,or a combination of both. For example, transcapacitive measurements canbe obtained between the sensor electrodes integrated within a displaydevice of the input device 100 and/or a dedicated force receiverelectrode. In another example embodiment, self-capacitive measurementscan be obtained using the sensor electrodes and/or the force electrode212. The sensor electrodes of the input device 100 can bend in responseto a force applied by an input object. The bending results in adeflection from equilibrium of at least a portion of the sensorelectrodes integrated within the display device. The deflection ofsensor electrode(s) due to the applied force changes the distancebetween at least one of the sensor electrodes and the one or more forcereceiver electrodes, which can be detected as a change intranscapacitance. The force information can include a “force image”,“force profile”, or a scalar force value, depending on the configurationof the sensor electrodes and the force electrodes 212. The forceinformation can be combined with position information to determine bothposition of one or more input object(s) and report an estimated forceapplied by each input object.

FIG. 3 is a block diagram depicting a cross-section 300 of the inputdevice 100 according to embodiments. The input device 100 includes aninput surface 301, a display cell 314 (also generally referred to as thedisplay 314), a backlight 308, an air gap/compressible layer 310, and atleast one force electrode 312. The input surface 301 can include atransparent substrate, such as a glass substrate. The force electrode(s)312 can be metal electrode(s). The force electrode(s) 312 may be onelarge conductive electrode or disposed as a plurality of conductiveelectrodes in any pattern. In some aspects, each of the conductiveelectrode(s) 312 can be a conductive, structural element of the inputdevice 100 that is re-used for influencing capacitive measurements toobtain force information, as discussed further below. In aspects, theforce electrode(s) 312 can be a metallic sheet. The force electrode(s)312 may be referred to as internal electrodes, an internal chassis,and/or a display chassis (e.g., of the backlight unit or of a fullmobile device).

In an aspect, the display cell 314 includes a color filter substrate 302(e.g., a color filter glass), inner layers 305, and a thin-filmtransistor (TFT) substrate 306. The inner layers 305 can include variouslayers, such as a color filter layer, liquid crystal display (LCD)material layer, conductive layers, dielectric layers, and the like. Inparticular, the inner layers 305 include one or more conductive layersforming sensor electrodes 304. The color filter substrate 302, the innerlayers 305, and the TFT substrate 306 are flexible such that the displaycell 314 is flexible. The layer 304 may be above, below, or within theinner layers 305.

The sensor electrodes 304 can have various configurations. In oneexample, the sensor electrodes 304 can include the plurality of sensorelectrodes 260 (or both the sensor electrodes 260 and the sensorelectrodes 270) in the sensor electrode pattern 250A. In anotherexample, the sensor electrodes 304 can include the sensor electrodes 210in the sensor electrode pattern 250B. In any configuration, the sensorelectrodes 304 can be disposed on the same layer or on different layers.In any configuration, at least a portion of the sensor electrodes 304can be common electrodes configured for display updating and capacitivesensing. In any configuration, at least a portion of the sensorelectrodes 304 also can be force electrodes 212 configured forcapacitive force sensing in addition to capacitive touch sensing.

The display cell 314 is disposed between the input surface 301 and thebacklight 308. The display cell 314 is flexible and can flex or bendwhen force is applied to the input surface 301. In the present example,the conductive electrode(s) 312 are separated from the backlight 308 bythe air gap/compressible layer 310, which can either be an air gap or alayer of compressible material. In other aspects, the backlight 308 andthe air gap/compressible layer 310 may be an integrated layer ofinsulated light-guide material. Accordingly, according to some aspects,the sensor electrodes 304 are disposed between the input surface 301 andthe force electrode(s) 312. The sensor electrodes 304 are configured todeflect toward the force electrode(s) 312 as the display cell 314 bendsinto the air gap/compressible layer 310 in response to a force appliedto the input surface 301. Depending on the location of the force appliedto the input surface 301, at least a portion of the sensor electrodes304 will deflect toward the force electrode(s) 312 in response to theapplied force.

The force electrode(s) 312 can be operated to influence the capacitivemeasurements obtained from the sensor electrodes 304 in response to theapplied force. Thus, the input device 100 can include force electrodes212, which include at least a portion of the sensor electrodes 304 andat least a portion of the conductive electrode(s) 312. In furtheraspects, some of the force electrodes 212, such as sensor electrodes304, are configured to deflect towards other force electrodes 212, suchas the conductive electrode(s) 312, in response to an applied force. Thedeflected force electrodes 212 (e.g., sensor electrodes 304) areconfigured for absolute capacitive sensing to determine forceinformation. The fixed force electrode(s) 212 (e.g., the forceelectrode(s) 312) can be operated as described below during the absolutecapacitive sensing.

While FIG. 3 illustrates one potential aspect, it should be understoodthat various other configurations may operate under the principlesdescribed herein. For example, in some embodiments, receiver electrodes(e.g., sensor electrodes 270) can be disposed on the color filtersubstrate 302 between the input surface 301 and the color filtersubstrate 302. In some embodiments, the force electrode(s) 312 can betransparent or substantially transparent and the backlight 308 can bedisposed beneath the conductive electrode(s) 312. In some embodiments,the force electrode(s) 312 are part of a chassis of the input device100. Alternatively, the force electrodes 312 can be disposed between thedisplay cell 314 and a chassis of the input device 100. In someembodiments discussed further below, a ground electrode 318 is disposedbetween the force electrode(s) 312 and a chassis of the input device100. Other types of flexible display cells can be used, such as an OLEDdisplay. In general, the display cell can include display pixels formedfrom LEDs, OLEDs, plasma cells, electronic ink elements, LCD components,or other suitable display pixel structures compatible with flexibledisplays.

According to aspects described in more detail, the sensor electrodes(e.g., sensor electrodes 304) and force electrode(s) (e.g., forceelectrode(s) 3112) can be operated (e.g., driven with signals) invarious manners to obtain different types of measurements. In somecases, the manner of operation may be based (e.g., dynamically) on anoperating state of the input device. For example, in a low power state,the input device may be operated for baseline force and touchmeasurements. In the presence of an input object, the input device maybe operated for touch and/or force measurements, and also may beoperated for interference measurements (e.g., periodically). In thepresence of interference, the input device may be operated to double thetouch and/or force signal. In some cases, the input device may operatein a time out state and perform no measurements.

Techniques described herein may provide for the sensor and forceelectrodes to be driven with alternating signals, such between asground, guard, and/or anti-guarding voltages in order to obtain touchonly measurements, force only measurements, and/or summed or differencedtouch and force measurements. According to aspects, by alternating thesignals, the measurements can be compared (e.g., added or subtracted) toisolate (i.e., differentiate) the touch/force measurements and, in somecases, to obtain twice the signal for a particular measurement (e.g.force). According to further aspects, in-phase and quadraturedemodulation of orthogonal waveforms can be used to obtain simultaneousand independent touch and force measurements.

Example Differential Touch and Force Sensing Using Anti-Guarding Signal

In the configuration of the input device 100 shown in FIG. 3, thecapacitance measurements detected (e.g., sensed) by the processingsystem 110 can include influences from both sides of the display 314.Thus, both touch effects and bending effects of force can be detected;however, distinguishing between the touch effects and the force effects,and compensating for mounting variations of the display 314, may bedifficult. For example, at start up time or test developmenttime/calibration, there may be no finger on the device to provide toucheffects. Therefore, the chassis may be measured relative to sensorelectrodes 304 (e.g., in the display). However, at other times, theremay be both touch effects and force effects. In some cases, anti-bendingtechniques, curvature methods, histogram methods, etc. can be used todistinguish between touch and force effects on the measured capacitance.

By differentially measuring back-coupled capacitance (i.e., thecapacitance coupled to the sensor electrodes 304 due to proximity withthe force electrode(s) 312), mounting variations, low grounded mass(LGM) through device coupling to the user input, interference, and fastmoving finger effects can be corrected. The touch effects on themeasured capacitance (referred to as the finger signal) may beseparately affected by LGM or interference, while the force effects onthe measured capacitance (referred to as the force signal) are mostaffected by the non-linear sensitivity of parallel plate capacitance todeflection.

According to certain aspects, while driving the touch sensingelectrode(s) (e.g., sensor electrodes 304) with a capacitive sensingsignal (e.g., referred to as a modulated reference voltage), a forceelectrode (e.g., a force electrode 312) can be driven alternately with aground signal/guard signal and an anti-guard signal in order to performdifferential touch and force sensing. As used herein, a “constantsignal” is a signal that is unmodulated with respect to a referencevoltage, such as system ground. A “ground signal” is a constant signalhaving an AC grounded voltage (e.g., the reference voltage or a voltageoffset from the reference voltage, the system ground, etc). A “modulatedsignal” or “modulating signal” is a signal that is modulated withrespect to the reference voltage (e.g., changes with respect to a“ground signal” over time). As described above, the capacitive sensingsignal can be a modulated signal or a constant signal. In an embodiment,a “guard signal” is a signal that is aligned (or substantially aligned)with the capacitive sensing signal in terms of amplitude and/or phase.For example, the guard signal can be a modulated signal that has thesame phase and the same or different amplitude (e.g., fractionalguarding or over guarding) as a modulated capacitive sensing signal. Inanother example, the guard signal can be a constant signal that has thesame modulation amplitude as a constant capacitive sensing signal (e.g.full guarding). In an embodiment, an “anti-guard signal” is a signalthat is not aligned with respect to the capacitive sensing signal (e.g.,inverted phase or opposite polarity). For example, the anti-guard signalcan be a modulated signal that is anti-phase (e.g., 180 degrees out ofphase) with a modulated capacitive sensing signal. The amplitude of themodulated anti-guard signal can be the same, more than, or a fraction(not zero) of the amplitude of the modulated capacitive sensing signal.In another example, the anti-guard signal can be a constant signal thathas an inverse voltage of a constant capacitive sensing signal. The term“anti-phase” includes phase alignment between signals that issubstantially 180 degrees.

According to certain aspects, by driving the force electrode (e.g.,force electrode 312) for force sensing, rather than the device chassis,then the chassis may be coupled to system ground, and the forceelectrode may be modulated relative to the chassis and the display. Inthis case, it is possible to measure force, finger, or force and finger.For example, by not modulating the sensor electrodes 304 relative to theground and modulating the force electrode relative to the ground, theforce signal alone can be measured. Alternatively, by modulating thesensor electrodes 304 relative to the ground and not modulating theforce electrode 312 relative to the ground, the touch signal alone canbe measured. Alternatively, by modulating both the sensor electrodes 304and the force electrode 312 relative to the ground, for example, byfully guarding the sensor electrode modulated reference voltage, thetouch signal alone can be measured. Alternatively, by modulating thesensor electrodes 304 and the force electrode 312 in opposite directions(e.g., modulated reference and anti-guard), the force signal can bedoubled and summed with a touch signal can be obtained.

In one example implementation, illustrated in FIG. 4, the input device400 may include display lens 401, display/sensor electrodes 414,backlight 408, air gap 410, force electrode 412, and case 416, and anoutput generator which includes an inverter 418 and a signal generator420. The display lens 401 may correspond to the input surface 301illustrated in FIG. 3. The display/sensor electrodes 414 may correspondto the display 314A including sensor electrodes 304, the backlight 408may correspond to the backlight 308, the force electrode may correspondto the force electrode(s) 312 and the case 416 may correspond to theground electrode(s) 318 and chassis. The case 416 may be an externalchassis of the input device 400 and may be coupled to the system ground.

As shown in FIG. 4, the force electrode 412 may be an internal electrodeor an internal display chassis of the input device 400. As shown in FIG.4, the output generator can drive the force electrode 412 with analternating guard and anti-guard signal. For example, the signalgenerator 420 can generate a signal, such as the guard signal 424 (ofthe same phase and amplitude as the modulated reference on 414), whichthe inverter 418 can switch to the anti-guard signal 422 (e.g., usingsimilar rails and inverting the signal output between two availableguard voltage rails). The force electrode 412 may be driven by the guardsignal 424 and/or the anti-guard signal 422 while the sensor electrodes424 are being driven with a modulated reference sensing signal (e.g.,Vmod) or with a constant reference signal (e.g., ground). For example, aswitch (SW) may be controlled by the processing system 110 or anexternal testing module to alternate between the guard and anti-guardsignals. Changes in capacitance of the sensor electrodes 414 can bemeasured while the force electrode is being driven by the guard andanti-guard signal.

In some cases, the switch (SW) can be moved between the two stages(guard and anti-guard) depending on what is to be measured. For example,while the force electrode 412 is driven with the guard signal 424, theresulting signal may correspond to a touch-only measurement. Whendriving the force electrode with the ground signal, the signal may beVmod. According to certain aspects, a guard signal may be similar to thevoltage modulated on the sensing (e.g. segmented Vcom) electrodes. Forexample, the guard signal may be equal in phase and/or amplitude to themodulated sensing signal on the sensing electrodes.

If a guard signal is applied to the device chassis (e.g., the metalframe) of the input device, the guard signal may minimize the effect ofthe housing. For example, the guard signal may be generated by the samecomplementary output generator (COG) used by the sensor circuitry 204 tomeasure the touch signal, or it can be generated by another applicationspecific integrated circuit (ASIC) separate from the sensor circuitry204.

On the other hand, while the force electrode 412 is driven with theanti-guarding signal 422, the resulting signal may correspond to a touchand force measurement. According to aspects, by alternating the drivingsignals, the resulting signals can be combined/compared (e.g., byaddition or subtraction) to obtain other measurements, such as doublethe force measurement. By driving the force electrode with theanti-guard signal, the resulting force signal may be equal to 2 Vmod. Asdescribed above, using the anti-guard signal for driving the forceelectrode may approximately double the sensitivity of the sensorcircuitry 204 to force deflections (e.g., doubles the force signal).Using the anti-guard signal may reduce scale factor errors in estimatinghousing (e.g., air-gap or foam) capacitance used for calibration.Dynamic correction of air-gap distance, for example, while the inputdevice is held in the hand may be easier because both ground andanti-guard do not risk guard-user coupling (e.g., through contact orLGM) and reducing the finger coupled signal below touch thresholds.

According to certain aspects, scaling of the anti-guard signal can befractional integers, multiple integers, or any rational number. Eitherpositive or negative polarity can be used. Ground is the case of zeroscaling and full guard is the case of 1 scaling. While −1 scaling isprimarily described herein, the scaling could also be −½, ⅓, 2, −3,etc., limited by the voltage modulation range and accuracy of theanti-guard drive electronics. According to certain aspects, an internalor external inverting or non-inverting amplifier may be used to generatethe anti-guard signal.

In another example implementation shown in FIG. 5, the force electrode412 may be driven by a signal that alternates (e.g., switches) betweenground (e.g., a constant voltage) and anti-guard (e.g., 180 degrees outof phase with respect to the modulating voltage driving the sensorelectrodes) signals. In this case, for example, while the forceelectrode 412 is driven with the ground/constant voltage signal 524,interference measurements can obtained.

In some cases, the input object (e.g., a finger) is moving and alsoapplying force. It may be desirable to measure the effects of finger andforce closely in time to minimize motion artifacts. According to certainaspects, this can be done by rapidly alternating between takingmeasurements while driving the force electrode (e.g., force electrode312 or 412) with the guard and anti-guard signal (in either order). Amultiplexer (mux) takes a multiple-input signal and provides a singleoutput. According to certain aspects, while using the same multiplexer(mux) settings to select measured touch electrodes, the processingsystem 110 can alternate between the guarded and anti-guard signalmeasurements. According to certain aspects, instead of performing thefinger measurements for an entire frame (e.g., 8 ms), the finger andforce measurements can be taken multiple times (e.g. at different muxlocations) in the scan of the touch frame (e.g., alternating everymillisecond). Alternatively, measurements (e.g. capacitive images) ofpreceding and following adjacent touch measurement frames can becombined to form the differential measurements to effectively calibratethe force deflection.

According to certain aspects, measurements of different parts of thearray pattern 250 can be performed in rapid succession (e.g., in onedisplay update frame) to compose one or more capacitive images. Forexample, the processing system 110 can alternate between touch and forcemeasurements. In one example, both force and touch can be measured overa portion of the array 250 at approximately a 1 ms time rate. Thus,multiple force and touch measurements may be taken faster than fingermovement. Because the measurements are taken in rapid succession, it maybe assumed that the finger has not changed position or force in thattime and the two are well correlated. By adding together sequentialtouch plus force and touch minus force measurements, a twice the touchsignal can be obtained, assuming force does not change. By subtractingthe touch plus force and touch minus force measurements, twice the forcesignal can be obtained, assuming touch does not change. Increasing thesignal may lead to improved signal to noise ratio (SNR) and filteringthe effect of interference. According to certain aspects, the processingsystem 110 can alternate between touch plus force and touch minus forcemeasurements. The results can be combined differentially to removechassis ccapacitive effects from the system.

FIG. 6 is a flow diagram illustrating example operations 600 fordifferential touch and force sensing using an anti-guarding signal,according to an aspect. The operations 600 can be performed by theprocessing system 110 described above to determine position information,force information, or both force information and position informationfor an input object interacting with the input device 100. In an aspect,processing system 110 performs all or a portion of the operations 1100during a non-display update time, such as a vertical blanking time or ahorizontal blanking time.

The operations 600 begin at step 602, where the processing system 110drives the sensor electrodes with a first modulated reference voltage(e.g., modulated with respect to the system ground). For example, theprocessing system 110 drives a plurality of sensor electrodes with afirst sensing signal, the plurality of sensor electrodes disposedbetween an input surface of the input device and at least one forceelectrode of the input device, the plurality of sensor electrodesconfigured to deflect toward the at least one force electrode inresponse to a force applied to the input surface. According to certainaspects, the first sensing signal may be a modulating signal (e.g.,Vmod) having a varying voltage. Alternatively, the first sensing signalmay be an AC ground having a constant voltage. The receiving sensors maybe modulated relative to the system ground (e.g., absolute capacitancemeasurement), or may be unmodulated (e.g. trans-capacitive measurement)relative to system ground while the transmitters are modulated.

At step 604, the processing system 110 alternately drives the forceelectrode(s) with second and third sensing signals (e.g. alternatingbetween ground/guard and anti-guard signals). For example, while drivingthe plurality of sensor electrodes with the first sensing signal, theprocessing system 110 drives the at least one force electrode byalternating between a second sensing signal (e.g. guarding voltagemodulation) and a third sensing signal (e.g. an anti-guarding voltagemodulation). In some aspects, the processing system 110 drives the atleast one force electrode with a constant voltage signal (e.g., ground)to acquire interference measurements and/or trans-capacitivemeasurements. The processing system 110 may alternate the forceelectrode quickly between the second sensing signal and the thirdsensing signal (e.g., multiple times in a single touch or display updateframe).

At step 606, the processing system 110 receives resulting signals fromthe sensor electrodes for both second and third force electrode signals.For example, the processing system 110 receives resulting signalscomprising effects of at least two of the modulated reference voltage,the guarding voltage, or the anti-guarding voltage.

At step 608, the processing system 110 determines at least position andforce information for an input object based on the resulting signals.

Example Simultaneous Touch and Force Sensing Using In-Phase QuadratureDemodulation

Typically, the touch signal (e.g., the finger signal) is detected bymeasuring the background capacitance and filtering it to estimate abaseline, and subtracting the baseline capacitance from all subsequentmeasurements to get the “future” finger signals. According to thetechniques provided herein, the background capacitance may be measuredsimultaneously and independently with the finger signal.

FIG. 7 is a block diagram depicting a simplified cross-section of aninput device 700 showing driving the sensor and force electrodes with amodulated sensing signal to acquire touch-to-sensor capacitive couplingand background capacitance, according to an aspect. As shown in FIG. 7,the baseline or background capacitance, C_(b), carries deflectioninformation (e.g., due to force of touch) between the touch sensorelectrodes 714 and the display chassis/ground 712. C_(b) is an additivequantity to the touch-to-sensor coupling capacitance, C_(t). Theresulting signal may be given by:

S(t)=(C _(t) +C _(b))V _(m)

According to certain aspects, in-phase and quadrature demodulation canbe used to obtain simultaneous and independent force and touchmeasurements. The sensor electrodes (e.g., sensor electrodes 304 or 414)and the force electrode(s) (e.g., force electrode 312 or 412) can bedriven with orthogonal (e.g., approximately 90 degree out-of-phase)signals. The signals can be orthogonal in frequency (e.g., where each ofthe orthogonal frequencies are outside the other's filter bandwidth),phase (e.g., one is Sine and the other in Cosine at the same frequency),or coded sequence (e.g. linear feedback shift register (LFSR), Barkercode, Hadamard codes, etc.). In such case, both signals can bedemodulated simultaneously.

According to certain aspects, in addition to the touch/display sensorelectrode 802 and force electrode 804, the input device may include adevice ground 806, such as ground electrode 318 (e.g., a conductiveplate or metallic sheet) between the device chassis and the forceelectrode, as shown in FIG. 8.

According to certain aspects, the resulting signal can be measured bythe sensor circuitry 204 (e.g., in some embodiments by AFE(s) 226),connected to the sensor electrodes. As shown in FIG. 8, C_(t) is thefinger-to-electrode coupling that provides the touch signal, and C_(b)is the background capacitance that provides the force information (e.g.,whether the sensor electrodes 414 and the force electrode 422 have beendeformed with respect to each other, for example by the force of touchby a user). V_(m) is the modulated signal, relative to the system ground806, used to drive the display sensor 802 and V_(mm) is the modulatedsignal, relative to the system ground, used to drive the force electrode804, where a component of V_(m) and V_(mm) are orthogonal in frequency,phase, or coded sequence.

As shown in FIG. 9A, two demodulators 908 and 910 can be used per sensorelectrode, for example, to measure both in-phase and quadrature (e.g.,I/Q demodulation) simultaneously. The signal Vm (Vref) (e.g., SIN) maybe driven onto the sensing electrode by the AFE 902, while a forceelectrode is modulated by signal Vmm (e.g., COS) and their summed chargeaccumulated on an RC feedback network (including capacitor 906 andresistor 904). By demodulating both phase (e.g. I/Q) signals andfiltering them, two independent localized measurements of Ct and Cb canbe made simultaneously and reported by the ADCs. The total charge (e.g.,the signal) S(t) received from the tixel (e.g., capacitive image pixel)upon touch can be given by:

S(t) = (C_(t) + C_(b))V_(m) − C_(b)V_(mm), where$V_{m} = {A\; {\sin \left( {2\pi \frac{t}{T}} \right)}}$$V_{mm} = {V_{m} + {A\; {\sin \left( {2\; \pi \frac{t - \phi}{T}} \right)}}}$

where T is the period of the oscillations, A is the amplitude, and φ isthe delay. Substituting V_(m) and V_(mm) into the equation for thesignal gives:

${S(t)} = {{C_{t}A\; {\sin \left( {2\pi \frac{t}{T}} \right)}} - {C_{b}A\; {\sin \left( {2\pi \frac{t - \phi}{T}} \right)}}}$

Demodulating the signal by in-phase and quadrature gives an in-phasecomponent:

$I = {{\frac{2}{T}{\int_{0}^{T}{{S(t)}{\sin \left( {2\pi \; \frac{t}{T}} \right)}{dt}}}} = {C_{t} - {C_{b}{\cos \left( {2\pi \frac{\phi}{T}} \right)}}}}$

and a quadrature component:

$Q = {{\frac{2}{T}{\int_{0}^{T}{{S(t)}{\cos \left( {2\pi \; \frac{t}{T}} \right)}{dt}}}} = {C_{b}{\sin \left( {2\pi \; \frac{\phi}{T}} \right)}}}$

where φ=T/4:

I=C _(t)

Q=C _(b)

Thus, the quantities C_(t) and C_(b) come out independent of each otherand can be measured simultaneously.

According to certain aspects, the demodulator can be in the modulatingcircuit itself (e.g., the output generator(s) 224). Another AFE can beadded in the modulating circuit to perform simultaneous I/Q demodulationon the ground electrode 318. In this case, another total force ofdeflection/deformation can be determined as a whole, rather than as afunction of position per sensor electrode.

As shown in FIG. 9B, guard and anti-guard signals may be alternatelydriven relative to system ground onto the force electrode using switches(e.g., switch 912 and switch 916) to modulate background capacitance Cb.The modulation (e.g., Vmod or Vref) of the sensing electrode allowsmeasurement of Ct from a user input. AFE 902 may sum the two charges byaccumulating charge onto a feedback capacitor 906, which may beintermittently (e.g. every measurement, every cycle, or half-cycle)reset with a reset switch 914. The output of the AFE 902 may bedemodulated with respect to the modulation of the sensing electrode andguard/anti-guard signals and filtered to provide homodyne measurementsand ADC results.

According to certain aspects, the touch signal and thebackground/baseline signal (e.g., the force signal) can bedifferentiated from each other (e.g., detected or separately sensed) ona localized per-sensor (e.g., per touch pixel) basis

FIG. 10 is a flow diagram illustrating example operations 1000 forsimultaneous touch and force sensing using in-phase and quadrature (I/Q)demodulation, according to an aspect. The operations 1000 can beperformed by the processing system 110 described above to simultaneouslyand independently determine both force information and positioninformation for an input object interacting with the input device 100.

The operations 1000 begins at step 1002, where the processing system 110acquires first resulting signal by driving the sensor electrodes with acapacitive sensing signal. For example, the processing system 110acquires first resulting signals by driving a plurality of sensorelectrodes with a modulated reference voltage, the plurality of sensorelectrodes disposed between an input surface of the input device and aforce electrode and configured to deflect toward the force electrode inresponse to a force applied to the input surface.

At step 1004, the processing system 110 acquires (e.g., simultaneously)second resulting signals by driving the force electrode(s) with anadditional orthogonal capacitive sensing signal. According to certainaspects, the force electrode is disposed between the input surface and asystem ground.

At step 1006, the processing system 110 determines positionalinformation for an input object based on the first and second resultingsignals. According to certain aspects, the processing system 110demodulates the first and second resulting signals to determine anin-phase component (e.g., an in-phase or quadrature component) of eachof the first resulting signals indicating changes in capacitance of theplurality of sensor electrodes and of the second resulting signalindicating a change in capacitance of the force electrode.

At step 1008, the processing system 110 determines force information foran input object based on the second resulting signals. According tocertain aspects, the processing system 110 demodulates the secondresulting signals to determine a quadrature component of the secondresulting signal indicating a change in capacitance of the forceelectrode.

In aspects, the quadrature demodulation gives an independent forcemeasurement. An independent and simultaneous touch measurement isobtained by subtracting the force measurement from the in-phasedemodulation.

The embodiments and examples set forth herein were presented in order tobest explain the embodiments in accordance with the present technologyand its particular application and to thereby enable those skilled inthe art to make and use the invention. However, those skilled in the artwill recognize that the foregoing description and examples have beenpresented for the purposes of illustration and example only. Thedescription as set forth is not intended to be exhaustive or to limitthe disclosure to the precise form disclosed.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

We claim:
 1. An input device, comprising: an input surface; at least oneforce electrode; a plurality of sensor electrodes disposed between theinput surface and the at least one force electrode, the plurality ofsensor electrodes configured to deflect toward the at least one forceelectrode in response to a force applied to the input surface; and aprocessing system coupled to the plurality of sensor electrodes, theprocessing system configured to: drive the plurality of sensorelectrodes with a modulated reference voltage; while driving theplurality of sensor electrodes with the modulated reference voltage,drive the at least one force electrode by alternating between a guardingvoltage and an anti-guarding voltage, wherein the guarding voltage isin-phase with respect to the modulated reference voltage, and whereinthe anti-guarding voltage is anti-phase with respect to the modulatedreference voltage; receive resulting signals comprising effects of userinput upon a coupling of at least one of the modulated referencevoltage, the guarding voltage, or the anti-guarding voltage, the effectsindicative of changes in capacitance of the plurality of sensorelectrodes; and determine both position information and forceinformation for an input object based on at least two of the resultingsignals.
 2. The input device of claim 1, wherein: the positioninformation is determined based on the resulting signal comprisingeffects of the user input upon the coupling of guarding voltage.
 3. Theinput device of claim 1, wherein the force information is determinedbased on subtracting the resulting signal comprising effects of the userinput upon the coupling of the anti-guarding voltage from the resultingsignal comprising effects of the user input upon the coupling ofguarding voltage.
 4. The input device of claim 1, wherein the processingsystem is further configured to: drive the plurality of sensorelectrodes and the at least one force electrode with a constant voltagesignal to acquire first changes of capacitance of the plurality ofsensor electrodes and the at least one force electrode; and determineinterference information for the input device based on the first changesin capacitance.
 5. The input device of claim 1, wherein the processingsystem is further configured to update a display, and wherein thealternating comprises alternating between the guarding voltage and theanti-guarding voltage multiple times in a single display update frame.6. The input device of claim 1, wherein the at least one force electrodecomprises an internal chassis of the input device.
 7. The input deviceof claim 1, wherein the at least one force electrode comprises atransmitter electrode and the plurality of sensor electrodes comprisereceiver electrodes.
 8. The input device of claim 1, wherein at leastone of the plurality of sensor electrodes is disposed on a color filterglass.
 9. The input device of claim 1, wherein the processing system isfurther configured to update a display, and wherein the plurality ofsensor electrodes comprises at least one common electrode configured fordisplay updating and capacitive sensing.
 10. A processing system for aninput device, comprising: sensor circuitry configured to: drive aplurality of sensor electrodes with a modulated reference voltage, theplurality of sensor electrodes disposed between an input surface of theinput device and at least one force electrode of the input device, theplurality of sensor electrodes configured to deflect toward the at leastone force electrode in response to a force applied to the input surface;while driving the plurality of sensor electrodes with the modulatedreference voltage, drive the at least one force electrode by alternatingbetween a guarding voltage and an anti-guarding voltage, wherein theguarding voltage is in-phase with respect to the modulated referencevoltage, and wherein the anti-guarding voltage is anti-phase withrespect to the modulated reference voltage; receive resulting signalscomprising effects of at least one of the modulated reference voltage,the guarding voltage, or the anti-guarding voltage, the effectsindicative of changes in capacitance of the plurality of sensorelectrodes; and a determination module coupled to the sensor circuitryand configured to determine both position information and forceinformation for an input object based on at least two of the resultingsignals.
 11. The processing system of claim 10, wherein thedetermination module is configured to: determine the positioninformation based on the resulting signal comprising effects of the userinput upon the coupling of the guarding voltage.
 12. The processingsystem of claim 10, wherein the determination module is configured to:determine the force information based on subtracting the resultingsignal comprising effects of the user input upon the coupling of theanti-guarding voltage from the resulting signal comprising effects ofthe user input upon the coupling of guarding voltage.
 13. The processingsystem of claim 10, wherein: the sensor circuitry is further configuredto drive the plurality of sensor electrodes and the at least one forceelectrode with a constant voltage signal to acquire first changes ofcapacitance of the plurality of sensor electrodes and the at least oneforce electrode; and the determination module is further configured todetermine interference information for the input device based on thefirst changes in capacitance.
 14. The processing system of claim 10,wherein the processing system is further configured to update a display,and wherein the alternating comprises alternating between the guardingvoltage and the anti-guarding voltage multiple times in a single displayupdate frame.
 15. The processing system of claim 10, wherein the atleast one force electrode comprises an internal chassis of the inputdevice.
 16. The processing system of claim 10, wherein the at least oneforce electrode comprises a transmitter electrode and the plurality ofsensor electrodes comprise receiver electrodes.
 17. The processingsystem of claim 10, wherein at least one of the plurality of sensorelectrodes is disposed on a color filter glass.
 18. The processingsystem of claim 10, wherein the processing system is further configuredto update a display, and wherein the plurality of sensor electrodescomprises at least one common electrode configured for display updatingand capacitive sensing.
 19. A method of operating an input device, themethod comprising: driving a plurality of sensor electrodes with amodulated reference voltage, the plurality of sensor electrodes disposedbetween an input surface of the input device and at least one forceelectrode of the input device, the plurality of sensor electrodesconfigured to deflect toward the at least one force electrode inresponse to a force applied to the input surface; while driving theplurality of sensor electrodes with the modulated reference voltage,driving the at least one force electrode by alternating between aguarding voltage and an anti-guarding voltage, wherein the guardingvoltage is in-phase with respect to the modulated reference voltage, andwherein the anti-guarding voltage is anti-phase with respect to themodulated reference voltage; receiving resulting signals comprisingeffects of at least one of the modulated reference voltage, the guardingvoltage, or the anti-guarding voltage, the effects indicative of changesin capacitance of the plurality of sensor electrodes; and determiningboth position information and force information for an input objectbased on at least two of the resulting signals.
 20. The method of claim19, wherein the determination of the position information is based onthe resulting signal comprising effects of the user input upon thecoupling of the guarding voltage.